Solution: Water PowerEdit
Energy in water can be harnessed and used, in the form of motive energy or temperature differences. Since water is about a thousand times heavier than air, even a slow flowing stream of water can yield great amounts of energy.
There are many forms:
- Hydroelectric energy, a term usually reserved for hydroelectric dams.
- Tidal power, which captures energy from the tides in vertical direction. Tides come in, raise water levels in a basin, and tides roll out. The water must pass through a turbine to get out of the basin. If the basin is a river delta then silt will block the turbine.
- Tidal stream power, Captures a stream of water as it is pushed horizontally around the world by tides.
- Wave power, which uses the energy in waves. The waves will usually make large pontoons go up and down in the water, leaving an area with no waves in the "shadow".
- Ocean thermal energy conversion (OTEC), which uses the temperature difference between the warmer surface of the ocean and the cool (or cold) lower recesses. To this end, it employs a cyclic heat engine.
- Deep lake water cooling, although not technically an energy generation method, can save a lot of energy in summer. It uses submerged pipes as a heat sink for climate control systems. Lake-bottom water is a year-round local constant of about 4 °C.
- Blue energy, the reverse of desalination. A difference in salt concentration exists between seawater and river water. This gradient can be utilized to generate electricity by separating positive and negative ions by ion specific membranes. Brackish water is produced. This form of energy is in research, costs are not the issue, tests on pollution of the membrane are in progress. At this moment it is predicted that if everything works out, 1/3 of the electricity needs in the Netherlands can be covered with this system.(2005)
Hydroelectric power is probably not a major option for the future of energy production in the developed nations because most major sites within these nations with the potential for harnessing gravity in this way are either already being exploited or are unavailable for other reasons such as environmental considerations. However, micro hydro may be an option for small scale applications such as single farms, homes or small businesses.
Building a dam often involves flooding large areas of land, this can change habitats so immensely that this risk of endangering local and non local wildlife is great. For example, since damming and redirecting the waters of the Platte River in Nebraska for agricultural and energy use, many native and migratory birds such as the Piping Plover and Sandhill Crane have become increasingly endangered.
Wave and tidal stream power schemes exist but require development capital.
OTEC has not been field tested on a large scale.
Critics of hydroelectric dams state that they may produce significant amounts of carbon dioxide and methane from rotting vegetation. In some cases produce more of these greenhouse gases than power plants running on fossil fuels. Dam failures, while rare, are potentially serious - the Banqiao Dam failure in China killed 171,000 people, many more than the immediate death toll in the Chernobyl disaster. (http://en.wikipedia.org/wiki/Renewable_energy)
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